This essay brievely explains the orientation effect of replacemen base

i. e

the replacement base consists of two groups

neighbour orientation base and intervalorientation baes

focusing on explaination of orientation effect with the modern theory ofresonance. That means that neighbour orientation base and interval orientation base can allbe considered as resonance body with resonance structure

among which three resonancestructures are leading contributors of variety of resonance

each of the three leadingcontributors of orientation base has a negative charge. That is why the favour-electricityreplacement effect happens to the neighbour or opposit parts. The neighbour or opposit partsof the leading contributors of the interval orientation base each has a positive charge

that iswhy the favour-electricity replacement effect chieflg happens to the interval part.In this essay

the author uses resonance theory to explain the orientation effect

different from the electronic-shift theory which is accepted by the textbooks.